The present invention relates, in general, to control units, and in particular, to a special configuration of a standard commercially available control unit so that an application specific processor need not be designed. In order to perform control functions, for example in motor vehicles, use is increasingly made of processor-controlled control units that control an automatic transmission or, alternatively, any other type of device. For this purpose, particularly when the functional scope and parameter range are known, it is preferable to use a standard commercially available control unit with a microcontroller and a memory, especially an external RAM module and flash memory. This results in a cost-effective design.
Problems can arise in the course of the application, for example, the adaptation of a control unit, in particular for a control unit of a transmission. For example, if a transmission specialist desires to adapt constants and characteristic curves for a specific type of motor vehicle, standard commercially available control units are not suitably designed for this application. For this purpose, control units with specially designed processors or other components have been applied heretofore. As an alternative to this, standard commercially available control units can be equipped with an additional memory in order to be able to utilize them at any time, but this is associated with additional technical complexity, costs and the required hardware and software. In this case, this additional memory (RAM module) can be inserted, for application purposes, into the area to be applied. It is also possible to use special control units in which the flash memory is completely replaced by a battery-buffered RAM memory. With these measures, although the application of the control unit is possible, for example in order to change characteristic curves during a motor vehicle journey, it is nonetheless associated with a high outlay.
German Patent Application DE 195 00 453 A1 discloses a control unit with a processor that does not have any chip select outputs. A decoder is provided for module selection. The decoder selects the assigned module according to the address transmitted on the address bus. At the output of the decoder, three chip select lines are provided. One serves for ROM selection, the second is used for RAM selection and the third is used in an application. The decoder is programmed in such a way that in the event of a desired application, the decoder always puts both the chip select line for the RAM selection and the chip select line for the application at the same potential. In this case, the chip select line for the application is connected to an address input of the RAM and consequently has the effect that only the memory area above this address value is used during the application.
It is accordingly an object of the invention to provide a new control unit with a standard commercially available processor, that overcomes the above mentioned disadvantageous of the heretofore known devices of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a control unit that includes a processor having at least a first chip select output and a second chip select output. A signal provided by the first chip select output is activated during a normal operating mode of the control unit, and a signal provided by the second chip select output is activated during an application mode of the control unit. The control unit also includes a RAM memory having a chip select input for selecting the RAM memory and having a memory area for use as an application memory. A combination element electrically couples the signal provided by the first chip select output and the signal provided by the second chip select output to the chip select input of the RAM memory such that the signal provided by the first chip select output and the signal provided by the second chip select output do not have a perturbing effect on each other. The memory area for use as an application memory is available as the application memory when the signal provided by the second chip select output is activated during the application mode of the control unit.
The new control unit enables the standard commercially available processor to be used to implement a specific application without requiring a specially designed processor and with a low hardware and software outlay and/or cost.
The control unit includes an external RAM module having a portion that can be used as application RAM. It is not necessary, therefore, to provide an additional RAM module. Since only a portion of the external RAM module is used as application RAM, the remaining portion of the external RAM module can be used for the customary purpose, for example for storing software variables. In this case, it is possible to define the portion used as application RAM in a freely positionable manner within the entire address range. Given appropriate structuring of the software, it is also possible to achieve a dual use of the application RAM. Software portions that are not used during the application or which can be deliberately dispensed with can use that portion of the external RAM module which is used as application RAM during normal operation (operating periods outside an application).
As discussed, the required hardware outlay is extremely low. The control unit merely requires a processor with an additional chip select line, an external RAM module, and a combination element for enabling the selection of the external RAM module with two chip select lines.
Consequently, the invention makes it possible to implement a special application with a control unit, for example for a transmission control, thereby making it possible to adapt constants and characteristic curves for a specific type of motor vehicle. This adaptation can be carried out while the motor vehicle is traveling, and the normal control functions of the control unit can also be carried out during the application phase.
In accordance with an added feature of the invention, the combination element is a logic element.
In accordance with an additional feature of the invention, the combination element is a logic OR element.
In accordance with a concomitant feature of the invention, the combination element is a logic AND element.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a control unit, in particular for use in a motor vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.